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At least 19 recordsLinked to original sources
PubMedDate not supplied

Inhibitory processes in the medial geniculate body.

Inhibition in the medial geniculate body was studied with a double click technique. A conditioning click caused a marked inhibition of field potentials and unit discharges to a subsequent test click. Cyclic inhibition with a period of about 150 ms was seen in the medial geniculate body and the auditory cortex, but not in the inferior colliculus. The postsynaptic excitability was tested by recording from the killed ends of the thalamocortical fibres. A preceding click reduced the direct response to a test stimulus delivered to the medial geniculate body indicating the presence of postsynaptic inhibition. The excitability of the fibres from the inferior colliculus terminating in the medial geniculate body was tested with a modified Wall (1958) method. The results suggest the presence of a presynaptic inhibitory mechanism in the medial geniculate body. The techniques employed do not allow an estimation of the relative contribution of the two inhibitory mechanisms to the inhibition at the medial geniculate level.

Acoustic Stimulation↗
PubMedDate not supplied

[Electrophysiologic relations in the lateral geniculate body].

Responses were evoked in the lateral geniculate body (L.G.B.) of "encéphale isolé" cats by single-shock stimulation of either the geniculate body or the optic tract of the other side. Responses to optic tract stimulation were modified following excitability changes in the contralateral L.G.B. due to topical application of strychnine and KCl. Laminar stimulation and recording in different layers (A, A1, and B) suggested the existence of a certain homotopic organization of L.G.B. interconnections. The activity evoked in the L.G.B. was found to be abolished by electrocoagulation of the posterior commissure and intermediate gray matter. These results point to the presence of a transthalamic pathway which might mediate L.G.B. activity to the contralateral visual cortex.

Animals↗
PubMed1979

[Electrophysiologic study of conduction of afferent impulses through the medial geniculate body].

In experiments carried out on cats immobilzed with d-tubocurarine 280 neurons located in pars principalis of the medial geniculate body and 408 auditory cortical neurons located in AI were studied extra- and intracellularly in response to stimulation of the brachium of the inferior colliculus and geniculocortical fibres. It was shown that the initial stage of the reaction observed in the medial geniculate body neurons response to stimulation of the brachium of the inferior colliculus continue for 13.0 ms. Excitation of 72% of neurons participating in the reaction occurs during the first 3 ms after stimulation. 84% of IPSPs arouse in the same period of time. It is found that some medial geniculate neurons have axons entering the inferior colliculus. Substantial part of fibres in the brachium of the inferior colliculus comes to the auditory cortex without synaptic switching in the medial geniculate body. 76% of medial geniculate neurons from the group excited monosynaptically are thalamocortical relay neurons and the rest are interneurons. 90% of relay neurons in the medial geniculate body are excited monosynaptically. Many medial geniculate neurons respond to stimulation of the brachium of the interior colliculus by EPSP-IPSP sequence or by primary IPSPs. About 20% of primary IPSPs develop monosynaptically. The maximal amount of IPSPs comes into being disynaptically with the participation of inhibitory interneuron located at the input to the medial geniculate body. The inhibition observed in this case is direct afferent one.

Action Potentials↗
PubMed1978

[Qualitative and quantitative studies on the lateral geniculate body in an ontogenic series of male Tupaia belangeri].

The cyto-, fibrillo- and myeloarchitectonics of the dorsal and ventral lateral geniculate body are described in an ontogenetic series of male Tupaia belangeri using light microscopy. The qualitative maturational changes show a heterochronical development. The ventral nucleus is developing earlier than the dorsal nucleus. A quantitative analysis of the fresh volume growth of the two brain regions also shows a heterochronical development. Two different kinds of growth curves were found. The dorsal lateral geniculate body has an overshooting growth which is approximated by the 6-parametric growth function: formula: (see text), The ventral lateral geniculate body shows a monotonously increasing s-shaped growth curve which is approximated by the generalized logistic growth function: formula: (see text), An analysis of the fresh volume growth of the six layers of the dorsal lateral geniculate body demonstrates all layers to take part in the overshooting growth type.

Animals↗
PubMed1978

Evidence for glutamate as a neurotransmitter in the corticofugal fibres to the dorsal lateral geniculate body and the superior colliculus in rats.

The high-affinity uptake of L-glutamate, D-aspartate and GABA were examined in homogenates from the dorsal lateral geniculate body and the superior colliculus after removal of the right visual cortex of adult rats. The high-affinity uptake of D-aspartate and L-glutamate were reduced by 53 to 75% respectively in the dorsal lateral geniculate body and by 46 and 53% respectively in the superior colliculus ipsilateral to the lesion. The uptake on the contralateral side was unaffected. The reductions were detected 3 days after the lesion and were maximally developed after 7 days. Subcellular fractionation showed that the main part of the uptake was confined to the synaptosomal fraction of both regions and that the reductions were most prominent in this fraction. The lesion was not accompanied by significant changes in high-affinity uptake of GABA nor in changes of choline acetyltransferase and glutamate decarboxylase activities. The high-affinity L-glutamate uptake on the contralateral visual cortex was unchanged from control values. After ablation of the visual cortex the level of L-glutamate was reduced by 32 and 17% in the ipsilateral dorsal lateral geniculate body and superior colliculus, respectively. The levels of the other amino acids examined, including L-aspartate, were unchanged. Enucleation had no effect on the uptake of L-glutamate and of GABA in the dorsal lateral geniculate body or in the superior colliculus.

Animals↗
PubMed1978

The medial geniculate body of the tree shrew, Tupaia glis. I. Cytoarchitecture and midbrain connections.

In this study of the medial geniculate body in the tree shrew eight subdivisions are identified on the basis of differences recognized in Nissl-stained material. Experiments using the methods of anterograde and retrograde axonal transport and anterograde degeneration show that each subdivision has a unique pattern of connections with the midbrain. The ventral division of the medial geniculate body contains at least two subdivisions, the ventral nucleus and the caudomarginal nucleus. The ventral nucleus is characterized by densely-packed cells and receives topographically organized projections from the central nucleus of the inferior colliculus. The caudomarginal nucleus, on the other hand, receives its major midbrain projections from the medial nucleus in the inferior colliculus. In the dorsal division four subdivisions are distinguished. The suprageniculate nucleus contains large, loosely-packed cells and receives projections from the deep layers of the superior colliculus and from the midbrain tegmentum. The dorsal nucleus receives projections from the midbrain tegmentum. The deep dorsal and anterodorsal nuclei have neurons which resemble those in the dorsal nucleus. Both receive projections from the roof nucleus of the inferior colliculus but the deep dorsal nucleus receives an additional projection from the parabrachial tegmentum. The medial division has a rostral and a caudal subdivision. The ascending projections to the rostral nucleus are from the lateral zone in the inferior colliculus and from the spinal cord. The caudal nucleus contains cells with large somas and receives projections from most of the midbrain areas which project to the other subdivisions of the medial geniculate body.

Animals↗
PubMed1979

[Cytochemical characteristics of the neurons of the external geniculate body in the rabbit brain in a period of visual function recovery after deprivation].

To study the properties of the external geniculate body, both neuron protein concentration and content were measured cytophotometrically in the cytoplasm of the above neurons taken from nomal animals and animals transported to normal conditions of illumination only after 2.5 months of visual deprivation, where they were put just after birth. The normalization of protein concentration and content has been observed in the neuron cytoplasm and in the surrounding structures. The magnitude of changes observed was related to the size of the neurons. It is supposed that some portion of neurons may exist in the external geniculate body having different degrees of dependence upon the visual impulsation. Mechanisms of possible rearrangement of the neuron metabolism in the geniculate body during the restoring period are discussed.

Animals↗
PubMed1978

The medial geniculate body of the tree shrew, Tupaia glis. II. Connections with the neocortex.

In this study the temporal cortex of the tree shrew was subdivided on the basis of cytoarchitectonic criteria, and the connections of each subdivision with the thalamus and midbrain were analyzed with retrograde and anterograde techniques. The results indicate that, with one exception, each subdivision of the medial geniculate body projects to a separate cortical area. The primary auditory cortex receives projections from the ventral nucleus. Surrounding the primary cortex are at least five additional cytoarchitectonically distinct areas which receive projections from the remaining medial geniculate subdivisions. The evidence suggests that there is very little overlap in the projections from each of these geniculate subdivisions. An exception is the projection of the caudal nucleus of the medial division. This subdivision apparently projects to most, if not all, of the cortical target of the medial geniculate body. Although the cortical projections of the caudal nucleus overlap those of the other medial geniculate subdivisions, the laminar distribution of its terminations in cortex is different. The caudal nucleus projects primarily to layer VI whereas the other subdivisions of the medial geniculate body project primarily to layer IV and the adjacent part of layer III. Anterograde techniques were also used to study the projections from the cortex back to the thalamus and to the midbrain. The projections to the thalamus precisely reciprocate the thalamocortical connections. The projections to the midbrain are to the same areas which the preceding study (Oliver and Hall, '78) showed give rise to ascending projections to the medial geniculate body. An exception is the central nucleus of the inferior colliculus which apparently does not receive a projection from the temporal cortex.

Animals↗
PubMed1979

[Response of pericruciate cortex neurons to stimulation of the medial geniculate body].

Electrical responses of 239 pericruciate neurons were studied in anaesthetized and curarized cats after stimulation of the medial geniculate body and medullary pyramids. The medial geniculate body stimulation evoked in the pericruciate neurons predominantly excitatory effects in the form of increase in the mean frequency of spike activity, generation of EPSPs and EPSPs-spike sequences. The latency analysis has shown that medial geniculate neurons have mono- and polysynaptic connections with pericruciate neurons not belonging to the pyramidal tract units.

Animals↗
PubMedDate not supplied

[Evoked potentials in the auditory cortex with systematic use of standard series of stimuli on the internal geniculate body].

Standard series of short electrical stimuli of the medial geniculate body were systematically applied to dogs with chronically implanted electrodes. Gradual formation was observed of a dependence of amplitudes of averaged EPs in the auditory cortex on the consecutive place of the stimulus in the series. This points to the existence in the dog's central nervous system of an elementary form of counting not only adequate signals, as has been previously shown, but also electrical stimuli of the thalamic nucleus. In contrast to what was observed in response to clicks, the EPs amplitude of MGB electrical stimulations increases by the middle of the series and diminishes by its end. It has been assumed that the cortical level of the analyser to which the stimulation was applied, suffices for the formation of the above phenomenon.

Animals↗
PubMedDate not supplied

Characteristics of excitation and inhibition of the receptive fields of the retina and lateral geniculate body.

The process of excitation and inhibition in the receptive fields (RF) of the ganglion cells and lateral geniculate body (LGB) of the cat were examined. The extent of the dependence of the magnitude of excitation and inhibition in RF on stimulus intensity was determined. This dependence is a power function with power indices of 0.15--0.20 (LGB) and 0.3--0.5 (retina) for excitation and 0.2--0.3 (LGB) and 0.5--0.6 (retina) for inhibition.

Animals↗
PubMed1976

Drugs and PGO waves in the lateral geniculate body of the curarized cat. V. Miscellaneous compounds. Synopsis of the role of central neurotransmitters on PGO wave activity.

In the last part of this series we have studied the effects of various drugs on ponto-geniculo-occipital (PGO) waves induced by the benzoquinolizine derivative, Ro 4-1284 (PGO(1284)), and by the inhibitor of trypotophan hydroxylase, p-chlorophenylalanine (PGO(PCPA)), and continuously recorder and counted in the lateral geniculate bodies (LGB) of unanaesthetized and immobilizedcats. The major aim of this study was to test the specificity of drug-induced alterations of the PGO wave activity suggested by the previous investigations. Hypnotics-sedatives of different classes had no significant effects in doses that did not markedly alter the electrical background activity in the LGB. A notable exception was gamma-hydroxybutyric acid which increased the density of PGO(1284) and PGO(PCPA). A number of neuroleptics were found inactive; sulpiride surprisingly decreased the density of PGO(1284). Bulbocapnine had a similar effect. Convulsants in subconvulsive doses did not uniformly affect PGO waves; while pentetrazole had no consistent effect, strychnine decreased and picrotoxin increased the density of PGO(1284). High doses of morphine, methadone and meperidine decreased the PGO(1284). Ethanol was inactive even in high doses. Caffeine and mefexamide reduced the density of PGO(1284). Mepiprazol was the most potent depressant of PGO(1284, probably by inhibiting the uptake of 5-HT. Mescaline was a weak depressor of PGO(1284). p-Chloromethamphetamine induced PGO waves in untreated cats less consitently than did PCPA. Amantadine reduced the amplitude of PGO waves due to a central antinicotinic action. The results of this study and of the whole series suggested a tentative scheme of the generation and modulation of PGO waves, in which the hypothetical roles and sites of action of four central neurotransmitters are included.

Amantadine↗
PubMed1976

Drugs and PGO waves in the lateral geniculate body of the curarized cat. I. PGO wave activity induced by Ro 43284 and by p-chlorophenylalanine (PCPA) as a basis for neuropharmacological studies.

Depletion, either predominantly of brain noradrenaline (NA) or preferentially of brain 5-hydroxytryptamine (5-HI), was achieved in cats by a single i.p. dose of 20 mg kg(-1) of Ro 4-1284, a benzoquinolizine derivative reducing the storage capacity of monoamine neurones, or by two i.p. injections of 300 mg kg(-1) of p-chlorophenylalanine (PCPA), an inhibitor of tryptophan hydroxylase. The ponto-geniculo-occipital (PGO) waves induced by these drugs (abbreviated PGO1284 and PGOPCPA, respectively) were continuously recorded from both lateral geniculate bodies of the unanaesthetized animals immobilized by gallamine. The present paper describes the characteristic qualitative and quantitative features of PGO1284 and PGOPCPA recorded under our standard experimental conditions; it provides the basis required for the following investigations of this series on the modulating effects of various drugs on this phasic brain activity. The density (number hr(-1) or number 0.5 hr(-1)) of PGO waves was inversely correlated with the levels of brain NA and 5-HT. At the peak of activity, during the second hr following the injection of Ro 4-1284, the density of PGO1284 was 630 hr(-1); it slightly declined during the following 5 hr. The highest activity of PGOPCPA (395 hr(-1)) appeared around the 74th hr after the first of 2 injections of PCPA; it remained constant for 3 hr and thereafter gradually declined. In constrst to the regular appearance of PGO1284, the PGOPCPA occurred in highly variable bursts. This difference was probably due to the different levels of NA and 5-HT in the brain.

2H-Benzo(a)quinolizin-2-ol, 2-Ethyl-1,3,4,6,7,11b-↗
PubMed1979

[Participation of the lateral geniculate body in color discrimination in cats].

Responses of the lateral geniculate units to different wave length stimuli were studied in immobilized cats. The studied units were divided into two groups. Those of the first group (44%) produce high-frequency spike discharges which are not modified when the wave length of stimulus changes. Statistically significant differences are found in the unit responses of the second group (51%) to different wave length stimuli. A possible inhibitory influence of the first group units on those of the second group is suggested. The possible significance of this influence in the colour vision is discussed.

Animals↗
PubMed1979

A quantitative study of chromatic organisation and receptive fields of cells in the lateral geniculate body of the rhesus monkey.

The responses of neurones in the lateral geniculate nucleus (LGN) were investigated in anaesthetised rhesus monkeys. A new classification for cells in the parvocellular layers (PCL) is proposed, based on their spectral response curve and their response to white stimuli: (A) narrow-band, short wavelength (NS) excited cells, activity suppressed by white stimuli; (B) wide-band, short-wavelength (WS) excited cells, excited by white stimuli; (C) wide-band, long-wavelength (WL) excited cells, (D) narrow-band, long-wavelength (NL) excited cells, activity suppressed by white stimuli; (E) light suppressed (LI) cells, activity suppressed by all wavelengths, usually with some concealed excitatory input at extreme short or long wavelengths. Responses to moving bars and to spots of various diameters (area response curves) were determined for various wavelengths. It was found that the receptive fields from which wavelength-dependent excitatory or suppressive effects could be elicited are concentrically superimposed. The spectral responsiveness of the excitatory inputs to individual cell types corresponds to the absorption curves of single cones (S-, M- or L-cone for NS, WS and WL cells respectively), the spectral distribution of the suppressive mechanisms of all cells was panchromatic and approximately fitted to a sum of all cones. The excitatory input to NL-cells cannot be related to any of the known cone absorption curves, and a simple (L-M) subtraction model is questioned. Neurones in the magnocellular layers (MCL) can be divided into on- and off-centre cells as in the cat's LGN and give qualitatively similar responses over the whole spectrum. In contrast to the tonic responses of PCL cells, MCL cells respond phasically to chromatic and white flashed spots, even with the smallest stimuli. Implications of these findings for colour processing in the LGN are discussed.

Animals↗